Post-operative MRI scans were performed on 12 patients, approximately 6 months after either a minimally invasive or open single level posterolateral lumbar spinal fusion (6 minimally invasive, 6 open). Edema and atrophy in the paraspinal muscles were evaluated using conventional MRI sequences, and quantitative differences were calculated using axial dual spin echo sequences and line scan diffusion-weighted imaging. Striking differences in muscle edema were demonstrated between the minimally invasive and open spinal groups. The mean T2 and ADC measurements were significantly lower in the minimally invasive group, suggesting that less muscle damage occurs using a minimally invasive approach.